Rootfs-v2021.1.22: Improve `recursively_regenerate_jlls.jl`

* Can now generate a temporary environment for you with all the
newly-regenerated JLLs

* properly de-jll's a parameter

PlatformSupport-v2021.1.22: LibGit2: fix for hostkey patch (#2434)

The previous version worked for explicit `ssh://` URLs but not for
`user@host` URLs that don't explicitly have the ssh protocol because the
`urldata` structure didn't have a `proto` field initialized. But we
don't actually need to use the `git_net_url_is_default_port` helper
since we already know that we're connecting via SSH. This version just
compares the `urldata.port` value with `SSH_DEFAULT_PORT` instead.

GCCBootstrap-v8.1.0+4

[qwtw] 3D lines/surfaces added (for linux only) (#2417)

GCCBootstrap-v7.1.0+4

[qwtw] 3D lines/surfaces added (for linux only) (#2417)

RustToolchain-v1.49.0: [RootFS] Install `samurai` instead of `ninja` (#2356)

Co-authored-by: Elliot Saba <staticfloat@gmail.com>

RustToolchain-v1.43.1+1

Update libsingular to 0.5 for Julia 1.5 (#2381)

RustToolchain-v1.43.1+0

Update libsingular to 0.5 for Julia 1.5 (#2381)

RustBase-v1.49.0

Update libsingular to 0.5 for Julia 1.5 (#2381)

RustBase-v1.43.1+0

Update libsingular to 0.5 for Julia 1.5 (#2381)

RustBase-v1.43.1

Update libsingular to 0.5 for Julia 1.5 (#2381)